This invention relates to electrical stimulation of animal cells, particularly human brain and heart electrical stimulation, including spine and other types of neurons, other types of muscles and organs like bladder and stomach, and in particular to the possibility of partial obstruction of the current induced in same by electromagnetic radiation, e.g., induced during MRI (Magnetic Resonance Imaging).
In the body of this patent we will be using the word “radiation”, which is a widely used term with many meanings, here used as EM (electromagnetic) radiation only. Note that “radiation” is often used as a short for “ionizing radiation”, as gamma rays, which can cause cancer. The frequencies used in our case are non-ionizing, so radiation used in this context is not cancer-causing agent.
Telemetry, used in the context of implanted devices for DBS, means the transmission of information using EM waves or any similar action-at-a-distance physical phenomenon, to send instructions to modify the state of operation of the device. Typically the instructions are send to the microcontroller embedded in the battery/electronics pack located in the chest, but nothing forbids other receiving units in other locations.
Several types of implanted devices for the purpose of delivering electrical pulses to different parts of the body have become practical, the most ubiquitous of which being the cardiac pacemaker, but also including DBS (Deep Brain Stimulation) and other neuronal stimulating devices, as for pain control, and other stimulators in the brain and peripheral nervous system as well, and also for other needs, as bowl control and the like. One of the disadvantages of wearing some of these, is their propensity to absorb electromagnetic waves (EM waves), which are induced AC, which is subsequently released as heat in localized spots in the wearer's body, with potential for discomfort, pain, or worse, depending on the temperature increase, or electrical interference with normal neural signals. In heart pacemakers another type of danger exists, which is the transfer of induced voltage on the connecting wires to the heart, or worse, to the heart sinus pacemaker, which could induce unwanted and erratic heart beats with the potential of causing the heart to stop. In other words, the wirings act as an antenna that then is the origin of current pulses along the device. The danger also exists to totally or partly destroy the electronic circuit that controls the device if the electromagnetic induced (EM induced) AC propagates to it, with the potential of erratic electrical pulses, with unpredictable consequences, including death too. These implanted devices are generally composed of a battery and an electronic circuit, which is implanted near the skin, for easy access if a need arises for replacement, from where wires run to the desired electrical stimulation location, as heart, brain, spinal cord, etc. Unfortunately the connecting wires act as antennae for external electromagnetic radiation, which in turn cause an unwanted current to flow through the connecting wire, that ultimately may cause either battery or electronic circuit failure, if the pulse propagates towards the battery, or it may cause heating on the other extremity of the connecting wire, which may then be on or near the heart, brain, spinal cord, etc, wherever the stimulation happens to be. This problem may be especially acute in DBS, because the wires are longer, running from the chest to the top of the skull then down from the top, inside the skull to the bottom of the brain, making DBS a longer antenna for electromagnetic radiation than heart pacemakers are, which in turn causes more energy to be absorbed by the DBS than by the heart pacemakers. With heart pacemakers, on the other hand, though the wires are shorter, so the induced voltage is lower (also the induced energy), the very nature of the device, to pace the heart, with electrodes placed at the most efficient positions to influence the heart beat, any electrical induced voltage is potentially mortally dangerous because it can cause erratic heart beating.
Because of this possible danger, MRI images are often, or at least occasionally, avoided in patients that wear one of these implanted devices, particularly in DBS and heart pacemakers wearers, because of the longer wires on the former, and the rhythmic sensitivity of the latter. DBS wearers carry a longer antenna, from the battery/electronics in the chest with a wire running to the top of the head. Pacemakers, though having shorter wires, are less likely to develop higher power to cause dangerous heating but suffer from the danger of causing heart arrhythmias. This avoidance is a problem because implanted patients are exactly the older ones, which are the ones more likely to need imaging, X-Ray, MRI, sonography, etc. From these, MRI is the worse, because it subjects the patient to a radio frequency (RF), AC electromagnetic field (EM field or EMF) of frequency on the order of 50 MHz, a frequency range used by many communications devices exactly because the antennae are so effective in this range. Because of this, at the very least the medical practitioners are prone to avoid requesting an MRI imaging on patients wearing electrical stimulating implants, particularly on a DBS wearer, who is known to be implanted with a longer wire, more prone to absorb electromagnetic energy created by the MRI imaging system.
This problem is widely recognized in the literature, and much time has been devoted to its solution, yet a complete and inexpensive solution has been eluding the designers of electrical stimulating devices.
Mark Kroll et al. U.S. Pat. No. 7,369,898, May 6, 2008, recognizes the problem and teaches a method to prevent the controlling unit from being disturbed by the RF and then sending erratic stimulating pulses to the stimulation site that are not programmed in the device. Though this is an improvement, it still fails to even address the other problem of induced RF in the conducting wire that goes from the power pack box to the stimulation site. It is only a partial solution. Moreover, Kroll teaches a method that depends on the device itself recognizing the presence of strong magnetic field, then the presence of an RF, before it enters in a self-protective mode. This has the disadvantage of relying on an automatic response, which can fail to activate, as opposed to a human activated response, which can be checked by a trained professional. Above all, Kroll's solution, when and if it succeeds, is a protection for the battery and electronics package only, located in the patient chest, but not a solution for heating and unwanted electrical stimulation due to induced currents in the connecting wires. Indeed, the very solution proposed by Kroll indicates that though the community is aware of the problem and have been trying to solve it for a long time, the true solution has been eluding all, indicating the importance of an inventive, a creative solution for this problem.
Zeijlemaker et al. (U.S. Pat. No. 7,623,930, Nov. 24, 2009) discloses a coordination between the telemetry system and the MRI system with the view of minimizing the possible damage, but it fails to stop the current flow due to induced electromagnetic waves in the wires that comprise the implant device. It also points to the eagerness of the community to solve a serious problem that has been eluding the practitioners of the art.
These examples show that this is a crowded field, with many practitioners of the art trying to solve a serious problem associated with electrical implants interaction with the RF electromagnetic waves used in MRI imaging. Yet, in spite of so much search and resources through in the problem, its solution has been eluding all.